Paleomagnetic and 40Ar/39Ar age constraints on the timing of deposition of deep-water carbonates of the Kurnool Group (Cuddapah basin) and correlation across Proterozoic Purana successions of Southern India

Abstract

• Deep-water carbonates of Chhattisgarh, Cuddapah, Kaladgi-Bhima and Pranhita-Godavari basins reveal similar 1.19 Ga primary paleopoles. • There was a minimal drift of the Southern Indian craton around 1.19 Ga. • Existing 900 Ma-800 Ma ages for deep-water carbonates of Cuddapah and Kaladgi-Bhima basins reflect isotopic disturbances. The sedimentary basins of the Bastar and Dharwar cratons, namely Chhattisgarh, Cuddapah, Intravati, Kaladgi-Bhima, and Pranhita-Godavari are located to the south of the Central Indian Tectonic Zone. These Southern Purana basins host well-preserved successions that may be divided into four unconformity-bounded sequences (i.e., Sequences I to IV). Sequence III contains unique deep-water carbonate layers, among which the Narji Limestone in the Cuddapah basin is representative. These carbonate layers have been shown to be of Mesoproterozoic age in most basins. However, the age of the Narji Limestone is still debated. Here, we report a primary paleomagnetic pole (26.2°N, 063.2°E, A 95 = 13.7°) with a positive fold test from the Narji Limestone, and also a reset 40 Ar/ 39 Ar age of ∼800 Ma obtained on a glauconite. Our results, combined with existing paleomagnetic data indicate that the Narji Limestone and Sequence III carbonates of the other Southern Purana basins share a similar primary paleomagnetic signature. The paleomagnetic poles of these carbonates plot consistently, and are used to calculate a mean pole (36.3°N, 070.8°E, A 95 = 10.7°) that compares well with a ∼1.19 Ga Indian pole. Our results contradict the view that Sequence III carbonates of the individual Southern Purana basins were deposited at different times as previously inferred from geochronological data. Instead, we suggest that these carbonates represent interconnected successions deposited in middle to late Mesoproterozoic times during an extensive marine flooding event on the Southern India craton. Our results support the suggestion that the existing Neoproterozoic ages for Sequence III may reflect post-depositional events.